Most fluorescent lamps available for inducing tanning of human skin are designed to have a spectrum of Immediate Pigment Darkening (IPD), exemplified by the DIN Direct Pigmentation Spectrum 5031 of November 1979, and therefore, emit predominantly UVA (320 nanometers of 400 nanometers) radiation. Lamps of this design generally emit a minimum of UVB (260 nanometers to 320 nanometers) which is believed to cause the formation of melanin, the skin pigment which darkens in the tanning process, but also induces erythema (i.e., skin reddening). These lamp designs only darken the melanin already present in the skin layer and generate little or no new melanin. Formation of melanin (melanogenesis) is necessary to the development of a more permanent and natural tan than that resulting from IPD, and therefore, attaining the protection of the skin from over-exposure to sunlight, which is the reason for the skin's tanning mechanism.
An example of fluorescent lamps emitting predominantly UVA and a minimum of UVB is described in UK Patent Application No. GB2059147A.
Other fluorescent lamp designs used for suntanning are predominantly UVB emitters and result in melanogenesis but are also likely to result in erythema unless exposure times are very closely controlled. Even with close control of exposure, it is likely that these lamp designs will cause damage to the upper skin layers.
Some suntanning lamps have limited amounts of the longer wavelength portion of the ultraviolet spectrum (380 to 400 nanometers) since this portion of the spectrum contributes very little to tanning. However, it is believed that this portion of the sunlight spectrum is useful to the human body and it has been shown in the past that Rhodopsin photoregeneration occurs with emissions in this range.
It is desirable then to overcome the prior art by having a suntanning lamp that produces a controlled amount of UVB for melanogenesis, an amount of UVA sufficient to induce IPD and some emission in the 380 nanometer to 400 nanometer range for other healthful effects. It would be especially desirable to have a lamp with a spectral energy distribution that substantially approximates natural sunlight in the ultraviolet region below about 400 nanometers since it would result in a tan very similar to that obtained by sunlight exposure and should also result in other health benefits due to the ultraviolet portion of sunlight.